Ok, I've always been more of a software guy than an electronics man. Haven't really done any electronics for a year either and tonight I'm understanding why I didn't miss it that much... My servo battery pack died this evening and I figured slaughtering a 6V adaptor and connect the whole thing to my breadboard would be piece of cake but boy was I mistaken. Here's the setup:

Vanson Regulated 6V AD/DC 400mA

ServoPower and ground connected to Vanson adapters power and ground, signal connected to PORTD on MCU (stk500 board)

STK500 boardGround from PORTD to ground from Adaptor and Servo. Signal from PORTD to servo.

I must be missing something in the setup here, since the servo refuse to move. If I plug in a batterypack instead of the adaptor (same setup), everything is fine. I've checked voltages with multimeter and it's the same for batterypack and adaptor. Also checked with respect to both ground on adaptor side and from stk500 side to make sure ground is common. Any ideas? I'm going nuts here...

Sorry if I was unclear, what I meant was ground from development board is connected with ground from adaptor/servo. About using 7805 with appropriate caps, there's already voltage regulation on the stk500 board so the micro is fine. Don't have anything for mr Servo though... But I didn't use any caps with the batterypack so I thought I should be ok?

I don't know anything about the STK500 board or the Vanson. So I am just talking off the top of my head here. It sounds like the Vanson is just not filtered well enough and is also just too weak; 400mA is not much when you start talking about running motors. Since you have regulation on the stk500 board, 6 volts is just too low to feed it. Regulation does more than just change voltage, it also helps to kiil noise on the power rails.

Both adaptors are connected to the same power jack in the wall, mcu and servo share ground. Sorry for my late reply, I've been out of town for a few days.... (Please notify me if you need a picture of the setup)

Well the servo have zero load, and it works fine when I use a batterypack instead of the adaptor. I measured with a multimeter and found no weird voltages, it's about the same from the pack and adaptor. Well, maybe disconnecting everything and re-connecting it again helps.... As for using a 7805 for powering the micro, I really don't see the reason to do that when the micro is mounted in a socket on a 100 dollar well developed Atmel (AVR) board built for the sole purpose of making things like powering, output/input, serial communication etc easier. I put my trust in the Atmel electronic engineers here...

This means that your adapter is unable to supply enough volts and/or current. Using a multimeter would have told you this

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As for using a 7805 for powering the micro, I really don't see the reason to do that when the micro is mounted in a socket on a 100 dollar well developed Atmel (AVR) board built for the sole purpose of making things like powering, output/input, serial communication etc easier. I put my trust in the Atmel electronic engineers here...

If its well developed, it should have a voltage regulator built in. Does it?